1. Field of the Invention
The present invention relates to an aluminum bonding alloy excellent in pressure weldability, diffusion bondability and brazability not only to a non-aluminum metals such as steel, copper, nickel or titanium but also to aluminum, and a clad material and an aluminum bonding composite material each including a bonding alloy layer made of the bonding alloy.
2. Description of the Related Art
Aluminum is excellent in electric conductivity, workability and lightness, and therefore is used in many fields as a raw material of electrode materials, terminal materials, electrically conductive wire materials, etc. On the other hand, an aluminum material (a single-layer material) made of only aluminum is inferior in mechanical strength and corrosion resistance, and therefore a clad material is also often used that includes an aluminum layer made of aluminum and a non-aluminum metal layer made of stainless steel or nickel, with the layers being bonded together by pressure welding and diffusion bonding. Such a clad material is used as an electrically conductive material for a battery case, an electrode material, and a terminal material, etc.
Though the diffusion bondability of aluminum to nickel is relatively excellent, that of aluminum to stainless steel is less excellent than that of aluminum to nickel, and therefore a nickel layer, whose diffusion bondability is excellent to both of aluminum and stainless steel, may be provided between an aluminum layer and a stainless steel layer. For example, Japanese Laid-Open Patent Publication 2000-312979 and Japanese Laid-Open Patent Publication 2004-351460 each describe a clad material including an aluminum layer, a stainless steel layer, and a nickel layer provided between the aluminum layer and the stainless steel layer. Japanese Laid-Open Patent Publication 2004-106059 describes a clad material including an aluminum layer and a nickel layer directly pressure-welded and diffusion-bonded to the aluminum layer.
On the other hand, a power module which has a semiconductor device integrally provided with an aluminum cooler to cool down the semiconductor device has recently been used as an electronic part, and it is desired that its cooling performance is improved depending on increasing of its output. The power module has a structure including the aluminum cooler, a heat-diffusion facilitating layer (a heat spreader), a heat-conductive insulating substrate (referred to as a “DBA substrate”) and the semiconductor device, wherein the aluminum cooler and the heat-diffusion facilitating layer are brazed together, and the heat-conductive insulating substrate and the semiconductor device are soldered on the heat-diffusion facilitating layer sequentially in this order, as described in, for example, Japanese Laid-Open Patent Publication 2008-166356. The heat-diffusion facilitating layer is usually formed from a clad material that is formed by bonding an aluminum layer to a copper layer excellent in heat conductivity to each other through an iron layer or a nickel layer by means of pressure welding and diffusion bonding.
The power module is usually assembled as follows. The aluminum cooler and the aluminum layer of the heat-diffusion facilitating layer are brazed together. Thereafter, the heat-conductive insulating substrate is soldered onto the copper layer of the heat-diffusion facilitating layer, and the semiconductor device is further soldered onto the heat-conductive insulating substrate. Otherwise, the heat-conductive insulating substrate having the semiconductor device soldered thereto in advance may be soldered to the heat-diffusion facilitating layer. The heat-conductive insulating substrate has a structure formed by laminating aluminum layers on both sides of a ceramic layer of aluminum nitride, etc., and the both surfaces of the heat-conductive insulating substrate are usually nickel-plated to secure the solder wettability of the surfaces.
As described above, aluminum and nickel are each excellent in bondability, and therefore, generally, an aluminum layer and a nickel layer are directly bonded together, and a stainless layer is bonded to an aluminum layer through a nickel layer. When aluminum and copper are diffusion-bonded together, a highly fragile intermetallic compound is produced therebetween, and then aluminum and copper are unable to be directly bonded, but an aluminum layer and a copper layer are able to be bonded to each other by providing an iron layer or a nickel layer between the aluminum layer and the copper layer.
However, though an aluminum layer and a nickel layer, or an aluminum layer and an iron layer, are able to be bonded together by pressure welding and diffusion bonding, an Al—Ni-based or an Al—Fe-based intermetallic compound is produced due to a diffusion reaction between the aluminum layer and the nickel layer, or the aluminum layer and the iron layer. When these intermetallic compounds excessively grow, the bondability is significantly degraded. Hence, the diffusion-annealing condition for the diffusion bonding after the pressure welding usually needs to appropriately be controlled so that the intermetallic compound layer does not excessively grow.
As above, the aluminum cooler is brazed to the aluminum layer of the heat-diffusion facilitating layer included in the power module with an aluminum brazing material for bonding aluminum such as an Al—Si-based brazing material at about 600° C. During this brazing, the intermetallic compound layer that is produced during the diffusion bonding between the aluminum layer of the heat-diffusion facilitating layer and the nickel layer, or the aluminum layer and the iron layer, grows. Accordingly, the problem arises of impairing the bonding strength which is present before the brazing between the aluminum layer and the nickel layer in the heat-diffusion facilitating layer, or the aluminum layer and the iron layer due to the brazing.
Improvements are recently demanded of the fuel efficiency of cars, trucks, etc., from a viewpoint of an environmental measure. Accordingly, in order to reduce the weight of structural members of a car, etc., it has been considered to replace a steel material of which some of the structural members are made with an aluminum material, and this replacement is actually conducted. However, it is difficult to bond the steel material and the aluminum material together by welding or brazing, and under current circumstances, these materials are mainly coupled with a mechanical coupling means such as rivets, and bolts and nuts. Hence, it is necessary to decrease the degree of freedom in the designing and reduction of the productivity for an aluminum coupling composite material manufactured by coupling the steel material and the aluminum material together.